The Liaohe River is located in the middle and upper reaches and supplies the Khorchin sandy land. It is significant to study the runoff variation and its causes for water resources reasonable exploitation and eco-environment manage in the river basin. The climate change is attributed to hydro-thermal conditions change. The comparison way of cumulative slope change rate is improved, and runoff change, climate change and the contribution of human activities to runoff change are analyzed quantitatively based on the data from three typical hydrometric stations (Xiawa, Fushandi and Wudan) on the middle and upper reaches of the river. It is found that runoff has been decreased slowly for many years, including some increase due to precipitation increasing and some decrease due to air temperature rising. In the 2000s, runoff reached a minimum, 45.89%~82.13% of that in the 1990s. 1995 and 1998 were the runoff abrupt change years. From 1995 to 2010 (1999 to 2010) the climate change in the areas controlled by Xiawa, Fushandi and Wudan hydrometric stations contributed 41.57%、60.20% and 36.76%, respectively, to the runoff decrease, and the human activities contributed 58.43%、39.80% and 63.24%, respectively, to the runoff decrease, as compared with that from 1957 to 1994 (1957 to 1998).